Although a substantial empirical literature has found associations between judges’ political orientation and their judicial decisions, the nature of the relationship between policy preferences and constitutional reasoning remains unclear. In this experimental study, law students were asked to determine the constitutionality of a hypothetical law, where the policy implications of the law were manipulated while holding all legal evidence constant. The data indicate that, even with an incentive to select the ruling best supported by the legal evidence, liberal participants were more likely to overturn laws that decreased taxes than laws that increased taxes. The opposite pattern held for conservatives. The experimental manipulation significantly affected even those participants who believed their policy preferences had no influence on their constitutional decisions.